From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Investigation into the causes and prevention of Wraith servo judders.
| Identifier | ExFiles\Box 108\3\ scan0118 | |
| Date | 3rd March 1936 | |
| To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale} c. HS.{Lord Ernest Hives - Chair} c. Da.{Bernard Day - Chassis Design} c. Mx.{John H Maddocks - Chief Proving Officer} c. RM{William Robotham - Chief Engineer}/IMW.{Ivan M. Waller - Head of Chateauroux} 600a WRAITH SERVO JUDDERS. Following reports from France that the servo on 26.G.VI had been juddering, we have carried out a number of tests on 26.G.VI and 25.G.VI to see how these judders might occur. There are two possible causes of servo judders :- (1) Judders due to changes in the coefficient of friction with speed variation. (2) Judders due to mechanical reasons. The way in which judders occur in the two cases are as follows. (i) A.{Mr Adams} When water, or other fluid is present on the rubbing surface, it is possible for a fluid film to be built up and broken down, the film being most easily maintained when the rubbing speed is highest. This means that when the driven member of the servo is moving, during a judder vibration, in the opposite direction to the driving member, little force acts to prevent it doing so, but when moving in the same direction as the driving member, a considerable force helps it on. There is only one way to prevent judders due to this cause, and that is to keep fluid out of the servo. B. It is theoretically possible to obtain a judder if the friction characteristic is such that /u is a maximum when rubbing speed is a minimum, and vice-versa. Judders due to this cause have been occuring on 25.G.VI, the judder taking the form of a grunt when the car is being braked, from 1 m.p.h. down to rest, and also when the brake pedal is released slowly. We found, in this case, that removing the dust from the face of the V.M.30 liners did much to improve matters, that graphiting the surfaces entirely prevented the judder, and that the Halo 3L linings now | ||